Microbes in the Mix
“To thrive in a body, pathogens need to do more than manipulate cell signaling and outwit immune defenses. They also have to outcompete the body’s hordes of normal, friendly bacteria.” ~ Canadian molecular biologist Brett Finlay
Both for proper development and functioning, the immune system relies upon commensal microbes. Beneficial bacteria are essential for the development of innate immune cells.
“The microbiota facilitate immune system development.” ~ English biologist Katharine Coyte et al
To protect their community, commensal bacteria communicate with immune cells and can even induce production of immune system cells.
Individual bacteria can specifically influence particular branches of the immune system. ~ American pathologist Dan Littman
Functional relations between the microbiome and immune system is intricate. Each immune cell type is affected in a variety of ways, both operationally and genetically.
Some microbes exert a powerful influence, while others sustain far more subtle effects. Very few resident microbes fail to make their presence felt to the immune system.
The microbiome guides the immune system in attacking pathogens while tolerating the commensal community within. Some microbes focus on creating a hospitable environment for themselves, while other aim to foster hostility toward foreigners. Bacteria in the same species may work toward different goals in their discourses with immune cells. There is an evolutionary checks-and-balances mechanism that ensures no microbe dominates.
“Beneficial microbes are essential for optimal immune responses to viral infections. These microbes are our ‘brothers in arms’ in the fight against infectious diseases.” ~ American microbiologist David Artis
When infection strikes, microbiota actively join the fight to protect the homestead they share with their host.
Bacteria evolve quickly. Many thousands of generations of bacteria come and go in a single human life. That means that bacterial evolution takes place literally right under your nose, and everywhere else in the body. Bacteria evolve their genetic material based upon their environment, especially exposure to food. Human immune cells are also somewhat adaptable, but not nearly as quickly, nor extensively, as bacteria.
Microbiota evolve the human immune system based upon environmental circumstances. This includes diet, as food constantly introduces new microbes.
Human cell evolution has played a part in microbial relations. Each new infectious disease weeds out weak microbes, leaving only more resistant survivors to pass on a genetic heritage. By that process, generation after generation, the human population built genetic resistance to pathogenic microbes. At the same time, many microbes themselves evolved to be less virulent, and thus improve life for themselves and their hosts.
Commensal microbes coexist with a host’s cells without setting off an immune response, though how they do so remain speculative. Natural killer cells terminate any encountered host cell that does not wear a telltale badge. Commensal microbes apparently carry no such signification yet remain untargeted.
The immune system within the gut does react to the microbiome there, and can kill foreign cells, but response is limited to keeping gut microbes from entering general body circulation where they would be killed.
The digestive tract is especially rich with microbes. The gut has its own distinct intelligence system. There is localized recognition of the interdependent inhabitants there.
As with plants, the intelligence system of animals is thoroughly distributed throughout the body. The gut is one example of where the local intelligence system keeps tab on all neighborhood residents.